INTRODUCTION

What do you feel when you enter a virtual world? What creates the
experience of presence? What factors contribute to making you feel
like you are there1 ?

This manuscript offers a subjective explanation of presence in
which the yardstick to measure presence is applied not to assessing
how closely a virtual world mimics real world sensations, but instead
to analyzing the kinds of evidence a virtual experience provides to
participants which help convince them they are there. Sensory realism
is subsumed within this broader perspective, as one of the means
which contributes to the experience of presence. The effectiveness of
the illusion of presence created by a virtual world can be partially
assessed by studying visitors to virtual worlds' subjective
experience of how much they feel like they are there and what makes
them feel that way. This goes beyond traditional objective concerns
such as comparing output device characteristics to data on what the
average human eye can perceive.

THREE DIMENSIONS OF PRESENCE

The basic premise is that experiencing your own presence in VR is
like the process of discerning and validating the existence of self
in the natural world (which humans have engaged in since birth). A
sense of presence in a virtual world derives from feeling like you
exist within but as a separate entity from a virtual world that also
exists. The differentiation and experience of self may be enhanced if
other beings exist in the virtual world and if they appear to
recognize that you exist. It may be enhanced if the virtual
environment itself seems to acknowledge your existence. As a
framework to focus discussion, three dimensions of the subjective
experience of presence (of existing), personal, social and
environmental presence, will be defined.

Subjective personal presence is a measure of the extent to which
and the reasons why you feel like you are in a virtual world.
Possible reasons are myriad, for example:

I see my own hand in the world.

The virtual world gives me a sense of deja vu, as if I've been
here before.

Although the rules of this world are different than the laws
of physics in the real world, there seems to be a consistent
pattern which I can learn to recognize.

Researchers trying to analyze subjective presence in virtual
worlds can begin by trying to identify as many features of that world
as possible which might contribute to convincing someone that they
are there. Virtual world designers, when designing a new experience,
can seek to consciously add in features which enhance the sense of
presence. Perhaps small, inexpensive features which cost little in
terms of memory or processing speed can significantly enhance the
experience of presence.

Social presence refers to the extent to which other beings (living
or synthetic) also exist in the world and appear to react to you.
This is in some respects a subset of personal presence, discussed
separately to draw attention to the power it may have in enhancing
presence. Social presence may derive from conversing with other human
beings, or from interacting with animated characters. Someone or
something else which seems to believe that you are there may help
convince you that you are there.

Environmental presence refers to the extent to which the
environment itself appears to know that you are there and to react to
you. Perhaps lights turn on when you enter a room, or portals to
other worlds flash into existence when you draw near. The argument is
the same as for social presence. If the environment knows you are
there, that may contribute to you believing that you are there.

These dimensions of presence will be discussed in relation to
developments in VR research and development. Subsequently, two quite
different virtual experiences for which data has been collected
specifically for this purpose will be analyzed in terms of elements
which contribute to personal, social and environmental presence.

PERSONAL PRESENCE

Virtual reality research has focussed extensively on creating a
sense of personal presence by simulating as closely as possible the
range and intensity of stimuli human senses detect and interpret in
perceiving the natural world. The desire to create vivid artificial
sensory stimuli leads to a quest for 3D images and sounds,
photorealism, tactile and force feedback, and so forth. For example,
a central NASA objective in VR research has been "to develop a new
kind of interface that would be very closely matched to human sensory
and cognitive capabilities" (Fisher, 1990). John Walker at Autodesk,
Inc. (1990) describes part of their vision for VR: "The richness and
fidelity of a cyberspace system can be extended by providing better
three-dimensional imagery, sensing the user's pupil direction,
providing motion cues and force feedback, generating sound from
simulated sources, and further approximating reality almost without
bounds." Zeltzer (1992) proposes that presence should be measured by
the number and fidelity of sensory input and output channels. In some
ways it is already possible to provide stimuli that are totally
different from or exceed those a human experiences without the
benefit of an artificial interface. Would this enhance or detract
from the sense of presence?

Faced with technological limitations which prevent being able to
simultaneously simulate all aspects of human perception, the alchemy
of presence in VR is in part a science of tradeoffs. Which elements
are most critical to the experience of presence? When forced to
choose between responsiveness to motion and resolution of images,
developers are choosing responsiveness as the more important factor,
based on their own experiences and observations of others. Because he
considers motion responsiveness more critical than resolution, Carl
Tollander, Chief Scientist for Autodesk's CyberSpace project,
envisions a cyberspace which can run on a broad spectrum of
platforms, such that "the space adapts the display itself to the
resources available," holding as constant as possible speed of motion
and moving closer to visual realism as computer resources permit
(Folz, 1991). Howard Rheingold reached a similar conclusion,
describing his experience using a telepresence VR system which let
him move his head to control a robot 20 feet away from himself in a
Japanese laboratory. Moving his head turned the robot's video camera,
the output of which he saw through goggles. "The fact that the
goniometer and the control computer made for very close coupling
between my movements and the robot's movements was more important
than high-resolution video or 3D audio... " (Rheingold, 1991).

Immersion VR frequently uses head mounted display and position
trackers to place the participant inside a virtual environment. The
sense of inclusion within a virtual world which this technique
creates has a powerful personal impact. Three hundred participants in
Autodesk's cyberspace rated "being inside" the virtual world as the
most compelling aspect of the experience (Bricken, 1991). The virtual
world appears to respond to head movement in a familiar way (the way
the natural world does: not at all) and in a way which differentiates
self from world. You move and the world stays still.

Frequently, being inside a virtual world is accompanied by a
dynamic, artificial representation of some part of yourself-- most
often, a computer generated hand. Meredith Bricken (1991), describes
the experience of watching her dynamic self-representation hand
within a virtual world as "convincing evidence that you're There."
Perhaps it would feel even more like being there if you saw your real
hand in the virtual world. Held and Durlach (1992) suggest that
similarity of visual appearance of the operator and robot or virtual
body are important the the experience of presence. On the other hand,
Jaron Lanier (1990), expressed surprise at the ease with which people
adapted to inhabiting nonhuman shapes, such as lobsters, in virtual
worlds. These are interesting research issues related to personal
presence.

In immersion VR, a sense of personal presence is based in part on
simulating real world perceptions. You know you are "there" because
sounds and images in the virtual world respond like the real world to
your head movements. Seeing your virtual hand move when your real
hand moves adds to the illusion. An alternative approach to personal
presence which does not strive to precisely simulate reality is what
Michael Miller calls "second person VR," exemplified by some of the
work of Myron Krueger, Mandala, and ENTER Corporation. In second
person VR, you know you are there because you see yourself as part of
the scene. On one side of the room, you stand in front of a blue
background. You face a monitor and TV camera. On the monitor you see
yourself, but instead of being in front of the blue background, the
self you see is inside of a graphic or combined video/graphic virtual
world. Edge detection software keeps track of your location and
movement and allows you to interact with graphical objects on the
screen.

Experiencing second person VR is a curious, compelling
transformation which places you into a world on the computer screen.
William Bricken describes it as an out of body experience (Osgood,
1991). Your body moves much like it always does, except that while
you move you are also watching your "real self" (that being on the
screen) appearing in and interacting with a virtual world. Rather
than mimicking real world sensations, second person VR changes the
rules, and relies strongly on a "seeing is believing" argument to
induce a sense of personal presence. According to Krueger (1990), a
sufficient sense of presence was achieved that some people "reported
a sensation in their finger when they touched the image of another
person on the point...It is enough that individuals have a very
proprietary sense about their image. What happens to them, what
touches it, they feel."

What you see and what you don't see matters. Held and Durlach
(1992) point out that "artificial stimuli that signal the presence of
a display" should be minimized, and that measurement devices in the
virtual or teleworld should be well disguised or hidden. Not showing
the microphone and not shooting off the edge of the artificial set
are two trivial tenants of movie production. There is much to be
learned from movie making about invoking suspension of disbelief and
creating the sense of being there in virtual worlds. Sheridan (1992)
and Zeltzer (1992) both suggest that different kinds of virtual tasks
may have different optimal minimal fidelity requirements. Do the
tasks of learning or playing or being excited or amused require more
or less fidelity to achieve a sense of presence than the task of
flying through a molecule to determine its structure?

In telepresence, seeing your physical self from across the room
has the opposite effect but the same result. (You see yourself,
therefore you know you are NOT there.) According to Rheingold (1991),
"what you don't realize until you do it is that telepresence is a
form of out-of-the-body experience." Rheingold describes turning his
head which caused the robot he was looking through and controlling to
turn its cameras toward Rheingold's physical body. "He looked like me
and abstractly I could understand that he was me, but I know who me
is, and me is here. He, on the other hand, was there. It doesn't take
a high degree of verisimilitude to create a sense of remote
presence." Thus, seeing yourself in telepresence is evidence for the
proposition that the "real you" is not currently inhabiting your
body.

Familiarity with a virtual world may also contribute to personal
presence. Having "been there before" helps you believe you are there
again. Held and Durlach (1992) and Loomis (1992) suggest that the
sense of presence may increase with experience and practice.
Participants' expectations, based on prior experiences with virtual
worlds, may also be a factor. As the art of designing virtual worlds
which induce a strong sense of presence improves, your expectations
will rise, and experiences which may initially have seemed adequate
may suffer by comparison.

SOCIAL PRESENCE

The premise of social presence is simply that if other people are
in the virtual world, that is more evidence that the world exists. If
they ignore you, you begin to question your own existence. The
Hollywood fantasy theme of a human who becomes invisible to the rest
of the world, and is able to move freely around (and through) people,
exemplifies the experience of reduced presence in that kind of
hypothetical virtual world. However, if the others recognize you as
being in the virtual world with them and interact with you, that
offers further evidence that you exist. Philosophers discuss the
"social construction of reality," wherein societies play a role in
what is perceived as real, through interpersonal communication and
through mass media such as television (Hawkins & Pingree, 1982).
Here we acknowledge the social construction of virtual reality. If
you were the only human living in the natural world, you would likely
have considerably more doubt about your own existence than you do
now. A one person virtual world is like that. (Except that the "gods"
who created the virtual world and an audience of other humans waiting
for their turn are probably watching you, perhaps contributing to the
perceived reality in a perverse way.)

Multiperson virtual worlds have received some attention. VPL's
"RB2" (reality built for 2) allows 2 people to share the same virtual
environment. Lanier speaks of hope for VR to become a medium for
"post-symbolic communication" among people, in which they could
jointly create or modify virtual worlds from within those worlds
(Ted/2 Videodisc, 1990). VPL's proposed "Reality Net" would link VR
participants at remote locations. The HIT Lab in Washington is also
working with phone companies to explore Televirtuality systems which
connect remote participants (Jacobson, 1991).

Vincent John Vincent regularly combines two proximate Mandala
(second person VR) installations, using a video switcher to put
participants from the two different spaces into a the same virtual
screen and allowing them to interact with each other's screen self.
Krueger's artificial reality experiments have also often allowed two
or more individuals to interact in VideoPlace (Krueger, 1991).
Participants saw themselves and each other in a virtual world.
According to Krueger, "the sense of being together was very strong."

Social presence can also be created through computer generated
beings. Delaney (1992) describes a creature created for a VPL world
which is programmed to travel to wherever you are currently located
and then begin repeating the phrase "pick me up" until you pick it
up. As soon as the creature has been picked up, it starts repeatedly
saying "throw me." As soon as you throw it, it rushes back and
resumes begging to be picked up. Although this gets annoying quite
quickly, it does contribute to your sense that other beings notice
and react to their movement in the virtual world. The characteristics
of the agent and the interaction probably affect the strength of a
sense of social presence which is created.

ENVIRONMENTAL PRESENCE

Many virtual world prototypes are, from the perspective of
presence, unresponsive environments designed to "let you explore."
Many real world environments are not very responsive to human
presence. There are solid objects in the room and you probably can
move them or paint them. Sheridan (1992) proposes that the ability to
modify a virtual environment is a key component of presence. 3-D
modeled virtual environments tend to be so totally unaware of
observers' presence, that you can get lost inside of a couch or a
mountain if you are not careful to avoid crossing illogical
boundaries. Many virtual worlds cannot be modified. These factors
likely detract from a sense of presence. Some responsive virtual
environments are being developed. Warren Robinett at University of
North Carolina has created virtual vehicles and tools-- e.g., an
elevator, which takes you up when you enter it. The HIT Lab has a
ridable ferry in Virtual Seattle. A VPL demonstration kitchen
includes a switch to turn on and off a fan. Some UNC environments
give feedback, e.g., about the appropriateness of the position of a
molecule or laser beam. (Robinett, 1990; Media Magic Video, 1991).
Virtual worlds can also be designed to be more responsive than real
worlds. When you walk into a room in the real world, it does not
verbally or musically greet you or start raining. Virtual rooms
might. It is quite possible that a virtual world which is more
responsive than the real world could evoke a greater sense of
presence than a virtual world where the environment responds exactly
like the real world.

DESCRIPTIONS OF TWO
VIRTUALITIES

Having proposed a rationale to explain the experience of presence,
let us move from theory to data, presenting studies conducted by the
author of 2 virtualities: the BattleTech Center in Chicago and ENTER
3D Second Person VR demos at CyberArts '91. Following descriptions of
the scenarios, issues of presence will be highlighted.

BattleTech

Since August, 1990, the BattleTech Center in Chicago has been
transporting visitors to the year 3025, placing them in control of
BattleMech robots at war in a computer-generated terrain amidst
computer-generated weather conditions. For $7.00 per person,
uniformed crewmembers guide six players through a training and
strategy session and then escort them to individual cockpits with
multiple viewscreens and feedback mechanisms and more than 100
controls to navigate the terrain and fight each other's Mechs for 10
minutes. Somebody wins, others lose, and detailed statistics on the
battle are provided after (and during) the game.

For four weekdays and one Saturday in September, 1991, players
were given questionnaires developed at Michigan State University when
they purchased playing times, to be turned in after the game.
Demographics about the "inhabitants" of this one year old virtual
world, their reactions to it and their reasons for playing were
studied. A total of 312 completed questionnaires were collected, for
a completion rate of 34%. (One questionnaire was collected per
person; at least 45% of the 1644 games sold during the sample days
represented repeat plays within the sample period.) Different
questionnaires were administered for each of 3 classes of players:
novices, who had played 1 to 10 BattleTech games (n=223); veterans,
who had played 11 to 50 games (n=42); and masters, who had played
more than 50 games (n=47). Novices had played an average of 3 games
veterans averaged 23 games and masters had played an average of 228
games.

Ninety-three percent of the BattleTech players surveyed were male.
Less than 5% of players surveyed were under 12. One fourth were
between the ages of 13 and 17. One fifth were between 18 and 20. Half
of the players were over 20. Sixteen percent were over 30.

ENTER 3-D Second Person VR

At CyberArts '91 in Pasadena for 4 days in November, ENTER
Corporation and the Michigan State University Comm Tech Lab exhibited
3-D interactive 2nd person VR demos and conducted research on
participant reactions. Participants wore 3-D glasses and stood

in front of a blue curtain. The camera that was pointing at them
was chromakeyed2 over 3-D motion video scenes, so that they saw
themselves inside of the video worlds instead of in front of a blue
curtain on the monitor across the room. People were able to interact
with graphical objects that appeared with them on the screen as part
of the motion video backgrounds. This was the first time that 3-D
motion video has been integrated into second person virtual
experiences. (Most often, second person virtual worlds let
participants see themselves inside of a 16- or 32- color graphical
world.) We were hoping to enhance the sense of presence through
photorealism (achieved by using a motion video background) and by
having that video be 3-D rather than the usual 2-D television, using
ENTER's 3-D technology.

Participants could choose to swim undersea and befriend unusual
sea creatures, dance or wander peacefully through a Japanese garden,
or transform into Godzilla to terrorize downtown Tokyo while aliens
from outer space tried to stop them. A loose "narrative" story
unfolded, with opportunities for the participant to interact. For
example, in the undersea adventure, small animated octopuses swam out
into the 3-D undersea video scene and grabbed onto you. They could be
shaken off and would swim away, or the octopuses could be carried
around. A little later, a much larger animated octopus swam out and
grabbed you. A shark swam by, and you were swallowed by a graphical
whale, becoming stuck inside the whale until you discovered a way to
get out.

For the first two days of demos, what the participants saw on the
screen as a representation of their "self" was a one-color
silhouette, or shadow which obviously looked like them and moved as
they did. The second two days they saw their real, full color self.
These two conditions represent two options available in second person
VR hardware configurations The silhouette version is much less
expensive than the real self version. A question for this study was
how much of a difference it made in participants' sense of presence
to see their shadow or their real self.

Approximately 160 individuals entered one or more of these ±3
minute virtual experiences. One hundred and ten were given
questionnaires to fill out (in particularly busy moments,
questionnaires could not be distributed). Eighty-seven completed
questionnaires, for a response rate of 79%. Three-fourths of
CyberArts respondents were male. Average age was 34, ranging from 17
to 55.

PERSONAL PRESENCE

Mixing Physical and
Virtual Realities

The BattleTech Center in Chicago mixes physical and virtual
reality. The Center itself is consistent with the theme of the
virtual BattleTech experience. Uniformed crew take you to a training
center to view video of a nervous trainee being initiated by a tough
commander. The crew member then escorts you to your 'Mech cockpit.
Inside the cockpit you find more than 100 buttons, a primary and
secondary screen with 6 selectable inputs, foot pedals and a joystick
all of which are physical, not virtual. But they control your virtual
'Mech. You navigate, turning, stopping, starting and it appears
through your viewscreen that these events are occuring.

ENTER's Second Person VR contrasts sharply with the BattleTech
Center. If you look anywhere other than at the monitor in front of
you, you are overwhelmingly reminded that you are standing in front
of a blue curtain waving your hands in the air. When you look back at
the screen, you see yourself underwater grabbing an octopus. 71% of
those who tried the demos considered the "being on the screen" to be
their real self, rating their screen self either more real then the
"being the camera pointed at" (29%) or as real as the "being the
camera pointed at" (42%). Only 26% felt the being the camera pointed
at was their only real self. These data suggest that a sense of
presence in the world on the screen has been created by the
experience.

Immersion VR replaces physical world sensations with virtual ones.
Second person VR ignores real world sensations, suggesting an
alternative scenario. BattleTech mixes them. Within a virtual world,
mixing physical reality may add to the illusion up to a point, but it
also may hold back the full effect of leaving the physical world, and
impose other limitations. You are obviously not really inside of a
robot, sitting in a physical cockpit in the middle of a room. The
cockpit is always there, always the same, it cannot change during a
game. What difference would it make to enter a virtual cockpit?
Second person VR is an almost outrageous leap of faith, to transfer
your self into a world on the screen. But perhaps that leap is a
powerful first step to entering a virtual world. Like Peter Pan
thinking a happy thought, once you make that initial leap, reality
becomes plastic and you can fly.

Sensory Channels in VR

The "original" five senses no longer comprise an exhaustive list,
nor are they necessarily the most relevant way to assess virtual
experiences. Other new senses can be added in VR. In BattleTech there
are auditory, visual and tactile stimuli. The tactile sensations come
from touching buttons and joysticks in the physical cockpit. Thus,
they are like the physical world, except that they are not quite like
what driving a real cockpit would feel like. Visually, we are
accustomed to one set of stereoscopic eyes. In BattleTech, there is a
primary monaural eye (the main screen) which is always visible, and
selectable secondary "eyes" which show views looking down at yourself
from 20 feet above your head, or 50 feet above your head, showing
your own internal damage report or showing your weapon status.
Returning to the idea of personal presence, senses like the physical
world help convince you you are there. Perhaps being able to examine
your virtual self from new and different perspectives provides
additional evidence.

In the ENTER second person VR demos, there was only sight (on a
single screen) and sound. Yet touch occurred. The senses were
transferred. Instead of feeling touch, you saw and heard touch. (The
beings on the screen reacted visibly and auditorily when your screen
self touched them. In the case of octopuses, the swimming creature
stopped swimming, grabbed the part of your body that touched them,
made gurgling sounds, and hung on for the ride unless you shook them
off.) Respondents who completed surveys reported feeling both
physical and emotional responses when they touched animated graphical
objects in these worlds. The emotional responses were somewhat
stronger than the physical responses. Only 14% reported feeling no
emotional response when they interacted; 24% felt no physical
response. Feeling something when you see an object on the screen
touch your self helps convince you you are there.

Movement/Navigation

In BattleTech, you drive the 'Mech, moving forward, back, left,
right and rotating your "head." Your movement is unconstrained on the
ground plane. Freedom to navigate without running out of world may
enhance the sense of presence. The world must exist if you can go
anywhere you want in it.

In the second person VR demos, you could move anywhere on the
screen that you wanted, forward and back, left and right, watching
yourself assume different positions within the motion video scenes.
But if you walked any further than the edge of the screen, you
disappeared from the scene. Within the stage, movement was
potentially very free. One former dancer danced in the Japanese
Garden. Some people got very involved, moving a lot. But contrary to
our expectations of participants enthusiastically exploring 3-D video
space by walking around in it, about half stood in one place, barely
moving at all until encouraged to do so. Either the virtuality
itself, the novelty of the experience, or self consciousness from
being watched by 5 to 30 people inhibited movement in the world, and
probably reduced the sense of presence.

Feedback

In BattleTech, feedback occurs whenever you are dired at and
whenever you aim or fire at someone else. Firing weapons also results
in noises and visual effects. In fact, there is far more feedback
than new players can attend to. Novices were asked about the three
most basic forms of feedback: where they were in relation to other
players, when they hit another player, and when another player hit
them. 60% of novices said they could tell where other players were;
35% said they sometimes could tell, and 5% could not tell at all.
When you hit another player, there is textual message indicating what
happened to whom. 63% of novices could tell when they hit someone;
30% sometimes could; 7% could not. Feedback can contribute to
environmental and social presence, particularly if it is understood.
The BattleTech world is apparently keeping track of you and the
others and knows you by name. The others seem to be aware of you,
because they fire at you whenever they get into range.

In the second person VR demos, many participants expressed a
desire in the open ended questions for more and more tightly coupled
feedback. During part of the Godzilla experience, waving your arms
triggered screams and roars. In the Japanese Garden, movements
triggered music and scene changes. People wanted to know exactly what
action triggered what response. Direct, overt coupling of action and
reaction would have made them feel more like they were there.

Perceptual Richness

Ratings of how real the BattleTech world felt were stronger (2.8
out of 7, where 1 is VERY MUCH) than ratings of the extent the
BattleTech world responded like the real world (3.7). And there was
not much desire expressed to enhance the perceptual realism of
BattleTech. When I tried it, driving the 'Mech felt a little "laggy,"
not letting me turn as fast as it seemed I should be able to. One of
the master players explained that this was intentional, because it
takes time to turn a big 'Mech around. Perhaps a good story can cover
for a lack of perceptual richness.

Veterans and masters were asked how much they thought 11 possible
changes to BattleTech would enhance the experience. The most desired
changes were more variety, less cost, more players at a time, and
playing time of longer than 10 minutes (ranging from 9.4 to 7.9 out
of 10). 3-D images, motion simulators and totally new games were the
next tier (6.3 to 7.1). Being able to play from home was not rated
particularly high (4.9). But least desired changes were to wear 3D
goggles, to wear a data glove, and to have less complex cockpits (3.4
to 2.2). Similarly, on a masters-only write-in question asking what
they would change about BattleTech, the suggestions tended not to
address fundamental alterations in the game or how it is played. Only
two masters asked that BattleTech management work on "improving the
reality." The overall lack of desire expressed by BattleTech regulars
for radically improved realities may be somewhat disheartening to
virtual reality developers working hard to generate ever greater
realism. These findings suggest that there is more to presence than
reality.

Unlike the BattleTech players, CyberArts participants wanted
goggles and more realism. They already were experiencing themselves
in 3-D photorealistic motion video space for the first time, and they
wanted more. Respondents were asked whether they would prefer to
experience themselves in the 3-D world by wearing glasses and looking
at the screen as they did at CyberArts, or by wearing goggles that
fill their vision with what's on the screen, no matter which
direction they look. This question is complicated. It was intended to
begin to address the constraint of having to look straight ahead to
see a screen all the time. The vast majority of respondents (84%)
indicated they would prefer to wear goggles and be able to turn their
head in any direction, even though the video world they were seeing
would stay still, and they would watch themselves turning in a world
which did not move. None of them have actually tried this-- it
creates its own complications because you cannot see the real world
you are moving around in when your entire field of vision is taken up
by a virtual world. You enhance presence by removing competing real
world perceptions, but complicate presence by making the experience
even less like reality. Goggles versus single screen would be an
interesting second person VR experiment.

For whichever of the 3 experiences a participant tried, (Undersea
Adventure, Japanese Garden and Tokyo Godzilla), they were asked to
rate their enjoyment, on a scale from 0 to 10 with 10 being very
enjoyable. Those who experienced only their shadow on average rated
the experience 5.8, compared to average ratings of 8.0 for those who
saw their real self . Otherwise identical experiences were
considerably more enjoyable when you got to see your real self in the
world. In a seeing is believing world, seeing your real self gives
more evidence that you're really there.

Second person VR write-in suggestions were numerous, with more
interactivity mentioned by more than 70 percent, and more realism
expressed by about half, including 3-D graphics, real photos instead
of graphic objects, making the 3-D sound, tactile feedback, etc.
Greater perceptual richness was definitely desired. (These people
were attending a virtual reality trade show...)

SOCIAL PRESENCE

If participants have their way, VR will be a very social
technology. Both the BattleTech and CyberArts data identify
consistently strong desires for interacting with real humans in
addition to virtual beings and environments in VR.

In BattleTech, playing against and with other people was very
important. Just 2% of respondents would prefer to play against
computers only. 58% wanted to play against humans only, and 40%
wanted to play against a combination of computers and humans. In
general, respondents preferred playing on teams (71%) rather than
everyone against everyone (29%).

The BattleTech study results are corroborated by the CyberArts
findings. Respondents were given a list of different kinds of
experiences which could be created using this technology, and asked
to rate their likely enjoyment of each genre, where 10 is HIGHLY
ENJOYABLE and 0 is NOT ENJOYABLE AT ALL. The desire to have other,
real people in second person VR worlds with you is extremely strong.
Sixty-nine percent of respondents rated having multiple players in
the virtual world as highly enjoyable (9 or 10). The average rating
was 8.5. The second highest desired experience was to participate in
live events interactively, rated highly enjoyable by 61%, for an
average anticipated enjoyment level of 8.3 Although the popular
fiction and media images of virtual reality tend to portray people
moving away from the real world into imaginary worlds, these data
suggest that virtual worlds and virtual reality interfaces can serve
to connect people to other people and to world events in new ways. In
fact, people want that connection more than any other experience.
Placing more than one person in a virtual world may be an easy way to
induce a sense of presence regardless of the other perceptual
features of the world.

ENVIRONMENTAL PRESENCE

In BattleTech, the terrain is not particularly responsive, but the
system is aware of you at all times. It keeps score. After the game,
it generates a complete printout summarizing every shot fired by any
of the 6 concurrent players and what happened as a result of the
shot. The score comes as a surprize to players -- they eagerly await
the display which tells them how they and others did. And the
printouts are the most revealing of all. They actually provide an
external validation of the experience, making it more real. When
asked whether the printout matched what a novice player thought
happened, he answered "I have no idea what happened, but this will
tell me."

As mentioned under feedback, 3-D second person VR participants
overwhelmingly wished for MORE INTERACTIVITY. They wanted the
environments to be more responsive. They wanted to become more a part
of the video image than they already were. They wanted real, 3-D
photorealistic fish to swim in front of them which they could play
with. They wanted complex interactions. Presumably, this would
enhance their enjoyment and their sense of presence. They wanted the
holodeck...

CONCLUSIONS

William Bricken says that "psychology is the physics of virtual
reality" (SIGGRAPH Proceedings, 1990). This paper focuses that
psychology beyond perception, spotlighting a messy array of elements
tied together by the concept of validation of virtual existence. A
question to guide designers of virtual worlds is how do I convince
participants that they and the world exist? Research can address
issues of which elements matter more-- personal, social,
environmental. Two example studies are reported here. More specific
questions can now be framed to assess and compare the experience of
presence in its different forms.

Different personality types may be more or less receptive to
alternative types of virtual experiences and to various forms of
evidence of existence. Children and adults may apply very unrelated
criteria. Females and males may approach VR with different criteria
for "being there." No significant differences were found between
males and females responses to 2nd person VR at CyberArts. Many
significant gender differences were found in reactions to BattleTech.
They may have been reactions to the competitive, warlike nature of
the game, or to the type of VR. Educators and psychologists identify
different learning styles, such as preference for visual, auditory or
touch communication channels. An individual's preferred channel is
presumably the most convincing to them for creating a sense of
presence. Perhaps an imagination IQ test should be developed. Is one
person's experience of presence in a virtual world the same as
another's?

Hawkins, R. and Pingree, S. (1982). Television's influence on
social reality. In National Institute of Mental Health (Ed.)
Television and Behavior: Ten Years of Scientific Progress and
Implications for the Eighties: Volume 2, Technical Reviews, (pp.
224-247) Rockville, MD: National Institute of Mental Health.

1 Throughout this and my other manuscripts on virtual reality, I
violate the academic convention of formal third person language,
writing about what "I" or "you" experience rather than what "one"
experiences. I do this to emphasize the unusual and very direct
nature of entering a virtual world.

2 Chromakeying one video signal over another involves use of a
chromakey-capable video switcher which strips a predefined or
user-defined subset of the overall picture chromanence of one of the
two signals, and replaces all parts of the image that were comprised
of that chromanence setting with the other video signal. Typically
the color used is blue.